The invention relates to a process for the electrical excitation of a laser gas, in particular, of a CO.sub.2 --He--N.sub.2 mixture which is delivered at an angle, preferably, perpendicularly to the axial laser gas discharge segment and which is ignited by microwaves included at an angle, preferably, perpendicularly to the laser gas discharge segment.
Laser light is frequently produced in an optical resonator consisting of two reflectors and a laser-active medium by means of light amplification by stimulated emission.
The laser-active medium is formed from excited, atomic systems, in the case of the CO.sub.2 laser from excited CO.sub.2 molecules. The excitation often takes place with an electrical discharge. In igniting this discharge, the electrical field strength inside the discharge tube must assume much higher values than needed to maintain the discharge plasma. When microwaves strike the as yet not excited laser gas, the laser gas is ignited when there is a sufficient field strength so that a small plasma zone is produced. This plasma zone absorbs the microwaves, additional electrons are produced and the plasma zone spreads out until, at a certain electron density, the so-called "cut-off density", the microwaves are almost completely reflected by the plasma in the direction of the microwave transmitter. The electrical field strength between transmitter and the plasma grows and the plasma continues to spread in the direction of the microwave transmitter. This procedure continues until the microwave has reached the wall of the container of the microwave entry window.
The "cut-off density" so important for the application of the reflection is a function of the microwave frequency and the impact frequency between electrons and molecules. When this "cut-off density" is reached, a final state is attained in which the microwaves are wholly absorbed in the boundary layer of the wall and can no longer advance in the discharge space. The boundary layer of the wall continues to heat up which often leads to damage to the dielectric discharge tube and to the microwave window.
The publication, "Schock, W. Laser Kolloquium 85, 13 DFVLR-Institut Fuer Technische Physik" demonstrates that in the discharge segment of gas lasers with microwave excitation, a highly absorbing wall boundary layer with a high electron density develops which normally makes the laser operation ineffective. In order to circumvent the wall boundary layer, the German Research and Testing Institute for Air and Space Travel (DFVLR, Institut fuer Technische Physik) has made an effort to include the microwaves in a nozzle current with a large pressure difference. With a buildup of a high pressure behind the dielectric window, an ignition in this zone is prevented. The laser gas is ignited in the lower pressure zone behind the nozzle. At a microwave power of 4.75 KW, a continuous CO.sub.2 laser power of 340W at 7% efficiency can be at most obtained. Since the laser gas flows in the propagation direction of the microwaves and the resonator is perpendicular to the inhomogeneously developing laser-active medium and only comprises part thereof, the efficiency of this arrangement is low. The entire installation, as a result of the required great mass current and as a result of the large pressure differences is very cumbersome and expensive.
An article in the publication "Journal of Applied Physics" 49(7) July 1978, "Laser generation by pulsed 2.45 GHz microwave excitation of CO.sub.2 " by Handy and Brandelik, pages 3753 to 3756 discloses a process for microwave excitation of a gas laser which leads to a gas laser of a similar nature. With this gas laser, the microwaves penetrate the laser gas perpendicularly to the laser gas current which comes in at a discharge tube entry arranged perpendicularly to the microwave inclusion and goes out at a discharge tube exit arranged perpendicularly to the microwave inclusion. Based on this arrangement, the heated up plasma lies at the dielectric discharge tube wall and forms here a very highly absorbing wall boundary layer. This leads to a low efficiency of the gas laser and requires a cooling with nitrogen precooled to 200K.